[tip: locking/core] locking/ww_mutex: Abstract out the waiter iteration

["tip-bot2 for Peter Zijlstra" <tip-bot2@xxxxxxxxxxxxx>]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     23d599eb2377404100d0d1508e12b0a2c40b49b1
Gitweb:        https://git.kernel.org/tip/23d599eb2377404100d0d1508e12b0a2c40b49b1
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Sun, 15 Aug 2021 23:28:45 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 17 Aug 2021 19:04:52 +02:00

locking/ww_mutex: Abstract out the waiter iteration

Split out the waiter iteration functions so they can be substituted for a
rtmutex based ww_mutex later.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210815211304.509186185@xxxxxxxxxxxxx
---
 kernel/locking/ww_mutex.h | 57 +++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
index 6a98f3b..1cd178c 100644
--- a/kernel/locking/ww_mutex.h
+++ b/kernel/locking/ww_mutex.h
@@ -1,5 +1,49 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+static inline struct mutex_waiter *
+__ww_waiter_first(struct mutex *lock)
+{
+	struct mutex_waiter *w;
+
+	w = list_first_entry(&lock->wait_list, struct mutex_waiter, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
+{
+	w = list_next_entry(w, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
+{
+	w = list_prev_entry(w, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
+static inline struct mutex_waiter *
+__ww_waiter_last(struct mutex *lock)
+{
+	struct mutex_waiter *w;
+
+	w = list_last_entry(&lock->wait_list, struct mutex_waiter, list);
+	if (list_entry_is_head(w, &lock->wait_list, list))
+		return NULL;
+
+	return w;
+}
+
 /*
  * Wait-Die:
  *   The newer transactions are killed when:
@@ -161,7 +205,9 @@ __ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
 
 	lockdep_assert_held(&lock->wait_lock);
 
-	list_for_each_entry(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_first(lock); cur;
+	     cur = __ww_waiter_next(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;
 
@@ -263,8 +309,9 @@ __ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
 	 * If there is a waiter in front of us that has a context, then its
 	 * stamp is earlier than ours and we must kill ourself.
 	 */
-	cur = waiter;
-	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_prev(lock, waiter); cur;
+	     cur = __ww_waiter_prev(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;
 
@@ -309,7 +356,9 @@ __ww_mutex_add_waiter(struct mutex_waiter *waiter,
 	 * may wound the lock holder.
 	 */
 	pos = &lock->wait_list;
-	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
+	for (cur = __ww_waiter_last(lock); cur;
+	     cur = __ww_waiter_prev(lock, cur)) {
+
 		if (!cur->ww_ctx)
 			continue;